Estimation और capacity planning — अपेक्षित load, data volume, और resource आवश्यकताओं की गणना — system design का एक महत्वपूर्ण हिस्सा है। मोटे "back-of-the-envelope" गणनाएं डिज़ाइन निर्णयों को सूचित करती हैं (कितना स्केल करना है, क्या resources आवश्यक हैं) और design साक्षात्कारों में सामान्य हैं।
अनुमान क्यों महत्वपूर्ण है
Estimating scale informs DESIGN decisions:
→ how many servers? how much storage? what database? do you need sharding/caching?
→ understanding the SCALE (small vs massive) shapes the whole design
→ rough numbers guide whether/how to scale (don't over- or under-engineer)
क्या अनुमान लगाएं (back-of-the-envelope)
✓ TRAFFIC → users, requests/sec (QPS); read vs write ratio (e.g. 100:1 reads:writes)
→ peak vs average (design for peak); daily active users → requests
✓ STORAGE → data size per item × volume × growth over time → total storage (and growth rate)
✓ BANDWIDTH → data transferred per second (request size × QPS)
✓ MEMORY → cache size needed (e.g. cache the hot 20% of data)
→ rough estimates (order of magnitude) → good enough to inform design
